


Fireproof

by Impala_Chick



Category: Shadowhunters (TV), The Mortal Instruments Series - Cassandra Clare
Genre: Alternate Universe - Canon Divergence, Community: seasonofkink, Condoms, F/M, First Time, Getting Together, Het, Marking, Porn with Feelings, Runes, Sensation Play, Vaginal Sex, What-If
Language: English
Status: Completed
Published: 2019-01-19
Updated: 2019-01-19
Packaged: 2019-10-05 00:38:33
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,029
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17314793
Author URL: https://archiveofourown.org/users/Impala_Chick/pseuds/Impala_Chick
Summary: Everyone prepares to travel to Edom with Magnus, and Simon turns to Izzy in the calm before the storm. Izzy wishes that Simon could have his own runes to protect himself, so she gets creative with a sharpie.A canon divergent AU of season three, inspired by and based loosely on book canon.





	Fireproof

**Author's Note:**

  * For [Wendymypooh](https://archiveofourown.org/users/Wendymypooh/gifts).



> I hope you enjoy some smut! I wasn't sure, but Simon & Izzy are just so gorgeous together. 
> 
> Also written for the prompts marking, first time, and sensation play over at seasonofkink.

The night before they were to venture down to Edom, everyone was extremely somber. Simon supposed “venture” wasn’t the right word, but he didn’t want to think about it any more seriously than he had to. They were all gathered around in Magnus’ loft, trying to figure out a way to mentally prepare for what they knew they had to do. With everyone in such a tense mood, he felt the need to crack a joke, but nothing was coming to mind.

He looked over at Clary and Jace, who were staring intently at each other with depressed looks on their faces. Simon resisted the urge to tease them, and glanced over at Magnus and Alec. They looked no better off, but Magnus was pacing and Alec was counting his arrows instead of looking at Magnus. 

And then there was Izzy. 

She was bouncing her leg up and down, and kept sneaking glances at Simon. But he definitely caught her doing it at least twice. He wanted to talk to her and comfort her somehow, maybe make her laugh. 

“Izzy, you wanna -” Simon started to say as he nodded his head towards the hallway.

“Yes, please,” Izzy said as she jumped up. 

Simon got up, shoved his hands into his pockets, and wondered into one of Magnus’ spare bedrooms, Izzy on his heels. Simon expected Magnus to make some kind of snide remark, or at least tell them not to shut the door or something, but Magnus didn’t. Simon supposed that Magnus was more worried than the rest of them. He was the one who was going to have to face his father, and he might have more at stake than the rest of them. 

Izzy shut the door softly as Simon sat down on the bed. Izzy walked over and sat down next to him, her hands on her thighs.

“Damn, what a mood tonight, huh? I feel like I could hit one of them over the head and they wouldn’t even react,” Simon said. 

Izzy huffed a laugh as she looked over at him.

“I know, right? This mission has _at least_ a 30% chance of success, and we’ve literally walked into situations with worse odds,” Izzy said.

“Oh c’mon, I’d say at least 35%.” Simon smiled at her, hoping to make her laugh again. She didn’t, but she was still smiling, which was basically a win.

Izzy reached over and took Simon’s left hand. She squeezed his palm, her face darkening again. 

“Izzy, we’ll all be fine. There isn’t any other group of people I would to go to hell with. All of you are skilled Shadowhunters. Especially you,” Simon said. Izzy sighed, shaking her head slightly.

“It’s not - I mean, I agree with you,” she said with a grin. “But I always feel calm right before a mission, because there is a plan, and I know that I am going to execute that plan to the best of my ability. That’s all I _can_ do. But this time, the mission feels different. I feel different.” 

“We’ve got all night to talk about it and plan for more contingencies. I doubt anyone is going to be sleeping much tonight,” Simon said. As she held him tight, he was surprised to realize his hand felt warm. He had gotten used to his skin feeling cold all the time. 

Usually she was the calm, level-headed one who picked out her blades with a smile on her face, happy to prepare for battle. Her worry unsettled him. He dropped her hand and wrapped his arm around her shoulders to pull her close, not because she needed protecting but because he was trying to stave off his own fear. She melted against him, and put her chin on his shoulder.

“I wish I could do more to protect you,” she admitted, her breath hot against his neck. Simon shuddered involuntarily from the contact, his brain going down a totally inappropriate path. Izzy felt strong and solid in his arms, but she was wearing something that had a floral scent, soft and delicate. Izzy was always so many things at once, which used to intimidate Simon. Now, Izzy’s strength and softness comforted him. Simon sighed against her hair, and tried not to think about kissing her.

“You realize I’m immortal?” Simon pointed out. She huffed a laugh and pulled back a little to look at his face.

“But not unkillable,” she said. 

“True, but that just makes me like everyone else. Even Magnus,” Simon answered. 

“No, not like everyone else. You don’t have any runes. And Magnus has magic,” Izzy said. She got up from the bed and started pacing. 

“I don’t need that stuff. I can rely on my winning personality and my stunning good looks,” Simon said, trying to make Izzy laugh. It didn’t work. 

She stopped her pacing to face him. The soft light from the one nightstand lamp illuminated her fiercely protective expression, and she had never looked more like an avenging angel. He couldn’t help but stare.

“I wish I could guarantee your safety, somehow. My runes give me strength, and stealth, and speed. And so many other things that I can utilize when I need them. I feel more confident in myself because I have them.”

Simon cocked his head, considering. He had seen runes come in handy for all of them before, but he’d never thought about what it would be like to have runes of his own.

“I appreciate the thought. But I am going to do everything I can to stay alive tomorrow. And you have to promise me you’ll do the same,” Simon said earnestly. Izzy smiled at him.

Then, she put her hands on both of Simon’s thighs, and leaned down. Simon’s gaze flicked from her eyes, to her cheeks, to her lips, and she never took her eyes from his face. Something impalpable passed between them, and Simon felt like they were hanging on the edge of a cliff, but he was ready to jump. He inhaled sharply, and then Izzy pressed her lips to his. The kiss was so soft, and so gentle, that Simon wanted to rip his undead heart out and hand it to her right then and there.

“Are you okay with that?” Izzy said against his lips.

“Yes, absolutely on board. Totally,” Simon rambled. He snapped his mouth shut, but Izzy was watching him, smiling gently. 

She placed her hands on his cheeks, and it was slightly reminiscent of the first time he had met her, when he waited on her bed in her room. But the gesture was the only thing that was similar. For one thing, Simon was a vampire now and her hand felt much warmer than it had before. And for another, he and Izzy were much closer. Maybe not friends, exactly. But Simon didn’t want to be just friends with Izzy. 

Izzy’s eyes lit up as she watched him, like she had an idea.

“Wait here,” she said as she hurried out of the room. 

Simon watched her go, slightly worried. Had he annoyed her with his rambling? But before he could go too far down that path, Izzy was back and brandishing a black permanent marker.

Simon raised an eyebrow. “What’s that for?”

“Okay, don’t laugh.”

Simon drew his finger across his chest in the shape of an x and nodded solemnly. “Cross my heart.”

She looked shy as she bit her bottom lip, and Simon wanted so badly to kiss her again.

“You can’t have real runes. But can I… draw some on you?” Izzy asked hesitantly. 

“Where?” Simon asked. 

“Your chest?” She asked, uncapping the pen.

After only a moment’s hesitation, he started to like the idea of Izzy brandishing that marker and protecting him metaphorically, in the best way she knew how. Simon took off his shirt and threw it on the ground. Simon couldn’t help but grin at the way she stared, enjoying the fact that she seemed to enjoy the view. He put out her hand, and she took it. As Simon eased himself down on the bed, Izzy followed and sat up on her knees.

She leaned down over him, and uncapped the pen to brandish it with her right hand. Her other hand settled against his stomach, and Simon felt the cold tip of the pen press into the skin over his ribs and slide over his skin as she carefully drew a rune. She was concentrating intensely on her task, and her mouth was pressed into a thin line. Watching Izzy focus on his body like that was provocative.

“Done,” she said as she sat back on her knees, admiring her handiwork.

“What’s it for?” Simon asked as he got up on his elbows to look down at it.

“Fireproofing,” Izzy said softly as she capped the pen. Simon smiled at that. What a fitting choice. 

“You could, uh. Draw another one, if you want to,” Simon said as he looked over at her. He realized he craved the intensity with which she had looked at him as she drew. 

“Yeah? You liked it?” Izzy asked. She grinned at him and uncapped the pen again.

Simon nodded sheepishly. He knew the runes were powerless on his skin, but the fact that Izzy wanted to give them to him made him feel confident, like they could take on anything together. That, combined with the way she looked at him when she drew them, made the whole process sexy as hell.

She pressed the pen to his skin again, this time on his upper left arm. She drew with a flourish, and ran her hands over his arm as she worked. She looked down at him when she was done, her lips slightly parted. 

“You’re watching me,” she whispered.

“Do you not like it?” Simon asked, his voice husky. He couldn’t help it. Watching her draw on him was causing his mouth to dry up. 

“I like that you like it,” she admitted. “That one is for endurance.”

He gulped, and lay back down flat on his back, eager for her to keep drawing. Izzy leaned over him to draw on his right side, and her boobs pressed against his chest. Simon closed his eyes and focused on the weight of her breasts and the feel of the pen moving across skin, and he shuddered from the sensations.

He felt Izzy move away, and he cracked open an eye to look at her.

“Can I draw on your neck?” She asked and then bit at her bottom lip, nervous.

“Yes,” he said without hesitation. He didn’t even care that someone else might see the rune later. “Pick a good one,” he joked. 

Izzy grinned before she leaned down and pressed her lips to his throat. She mouthed along his jaw, and then kissed back down his neck. Simon groaned from the simple pleasure of it. He could smell her blood rushing through her veins, and he wanted to touch her, but he kept himself still.

“This one is for courage in combat,” she said. The cool tip of the pen replaced her warm lips, as she drew where she had kissed him. Simon moaned when the pen touched him, surprised at the contrast. 

“Touch me, Simon,” Izzy whispered in his ear. He surged forward to grab her thighs and pull her on top of him as he sat up. 

“Vampire strength,” he said, almost to himself. Izzy laughed, her eyes bright as she settled down into his lap. She looked so beautiful happy like that, it took his breath away.

“Careful, I might accidentally get a pen mark on your face,” she warned. She held the pen out to the side, and then she kissed him again, her arms around his shoulders. Simon rocked his hips up into her and moved his hands up to squeeze her ass. She pushed down against him and groaned into his mouth.

“Isabelle, you’re beautiful,” Simon whispered.

“You’re not so bad, Lewis,” she said. She pushed down against him again, and there was no way she didn’t notice his hard-on. He wanted to touch her everywhere at once, but he settled for sliding his hands up under her shirt to pull her to his chest. Izzy gripped his biceps and kissed his throat as they rocked back and forth like that. 

“Take off your pants,” Izzy panted, out of breath. She swung her leg off of him, and Simon scrambled to pop the buttons of his fly. He eventually had to tear his gaze away from Izzy to figure it out, and then he pushed his jeans down his thighs and kicked them off. He didn’t feel particularly sexy getting undressed, but then he looked up at Izzy. She was staring at him hungrily. He got up on all fours and crawled to Izzy so he could press his lips to hers. She laughed against his mouth. 

“Sexy crawl there, vampire.”

“You like?” He wiggled his eyebrows, and she laughed harder. She gently guided him down to the bed, and Simon felt his heart rate speed up as she ran her hand down his ribs, over the rune she drew earlier. She paused when her fingers met the waistband of his boxers.

“Just one more,” she said. He nodded eagerly, and sat up on his elbows to watch her. She skimmed her fingers over his hips, and then pressed the pen to his thigh, just below the edge of his boxers. She leaned down to draw, and Simon felt her breath ghost over his skin, right near his dick. He felt himself getting harder, and he was so hungry for her. He could hear her blood rushing through her veins, and he thought that might mean she was hungry for him too. 

“Isabelle, I want to fuck you,” he admitted. She looked up at him, her eyes wide. She capped the pen and put it down.

“Good thing I’m done, then.” She unzipped her jeans and kicked them off. She pulled a condom out of her pocket before throwing her jeans on the floor, and then she looked at him, a question in her eyes. Simon took the condom from her, grateful that she had one, and pulled down his boxers to expose his cock. Simon felt sexy because of the way she was watching him. Once he was done, she straddled Simon again. 

He surged up to run his fingers over her simple pink panties. He licked into her mouth, eager to please her. She balanced herself on her knees, and pushed her panties aside. She lowered herself onto the head of Simon’s cock, as Simon pulled her shirt over her head.

“Fuck,” he shuddered as he felt his cock enveloped by her cunt, wet and throbbing around him. He pulled her left breast out of her bra to lick her nipple, and she pushed up against his mouth with a moan.

“Oh my god, Simon.” Izzy’s head was thrown back and her hair fell all around her like a curtain as she pushed herself down to take more of Simon inside her. Simon wrapped one hand around her back to hold her steady, and she started to fuck herself on Simon’s cock, slowly at first.

He cupped her breast, and laved at her nipple. Her body weight pressed down against him, and her skin felt delightfully warm against his own. Simon moaned from the pleasure of it, and Izzy was watching him with her lips parted. She grinned wickedly before she started to ride him harder. Her cunt clenched Simon’s cock as she moved up and down, and Simon watched as she snaked her hand down to touch herself. He wondered if this was going to be enough for her. He felt so close already.

“Can you come on my cock?” Simon asked as she started to move his hips to meet her thrusts. Simon couldn’t look away from her fingers, pushed down her panties and drawing tight circles against her clit.

“Yeah, I think so. Just... fuck me like that,” Izzy breathed as she squeezed her eyes shut. Simon kept thrusting his hips up, and concentrated on keeping a steady rhythm. He gripped her hips and guided her movements. The way her cunt squeezing all around him was amazing, but he tried to keep his focus on her pleasure. He felt the moment she tumbled over the edge, because her cunt pulsed against his cock. The pressure against the head of his cock on every thrust was perfect. He fucked up into her as she threw her head back with a groan.

“By the Angel, Simon,” she mumbled. Simon’s eyes slid closed as he focused on the feeling of her cunt around his cock. Izzy slid her fingers over his bottom lip and Simon shuddered at the sudden warmth of her fingers. His thrusts became erratic as he lost himself in the feeling of fucking her.

“Come for me,” she whispered in his ear. He willingly obliged, and his mind went blissfully blank as he came. 

Once he opened his eyes, Izzy leaned down to kiss him. He sighed happily as she got up, and Simon tied the condom off before getting up from the bed.

“Hey,” she said. He turned around and let her pull him to the edge of the bed, and then she kissed him again. Simon melted against her, his body tingling with pleasure.

“Thank you,” he said against her lips, his voice reverent. She was still in her bra and panties, and Simon was still blown away by how beautiful she looked.

“For what?” she asked softly.

“For protecting me,” he said as he gestured at his marker runes. She smiled at him. 

“We’ll do this again, after we get back,” Izzy said firmly as she lightly traced the fireproofing rune over his ribs.

“After we get back,” Simon echoed. He kissed her forehead before turning to the bathroom, his heart full. He knew without a doubt that Izzy would do whatever she could to protect him as they walked through hell. And he would do the same.


End file.
